In the 1970s CPUs still had wildly different approaches to basic features, with the Intel 8086 being one of them. Whereas the 6502 used separate circuits for operations, and the Intel 8085 a clump of reconfigurable gates, the 8086 uses microcode that configures the ALU along with two lookup tables. This complexity is one of the reasons why the Intel 8086 is so unique, with [Ken Shirriff] taking an in-depth look at its workings on a functional and die-level. These lookup tables are used for the ALU configuration – as in the above schematic – making for a very flexible but also complex system, where the same microcode can be used by multiple instructions. Of course, as semiconductor technology improved, along with design technologies, many of these trade-offs and disadvantages became less relevant.